RF repeaters for time division duplex cordless telephone system

ABSTRACT

The object of the invention is to employ a single amplifier for both the transmit and the receive signals in an RF repeater for interfacing with a base station for exchanging transmit and receive signals in a time division duplex cordless telephone system. A multicarrier amplifier having an input and an output and a transfer switch connected to the amplifier output and the amplifier input and having first and second switch states. The operation of the switch is controlled so that the transmit and receive signals are amplified by the amplifier. The other object is to chain RF repeaters so that the handset can roam over a roamer corridor covered by the RF repeaters. The RF repeaters are provided with a dedicated signal link.

TECHNICAL FIELD

The present invention relates to RF repeaters for use in cordlesstelephone systems and, more particularly, for interfacing with cordlesshandsets and cordless base stations exchanging transmit and receivesignals using time division duplex transmissions and is also applicableto frequency division duplex (FDD) transmissions.

The present RF repeater is useful in particular in telephone systemsemploying cable television plant as a signal conduit but may also beemployed in cordless telephone systems utilizing dedicated coaxial cableand/or fibre optic and/or microwave signal conduits.

BACKGROUND ART

It is expected that Personal Communication Services (PCS) microcellswill be supporting a rapidly increasing number of handsets in NorthAmerica in the near future. To support this user base it is essentialthat the PCS microcells be both low power to assist frequency re-use andlow cost, because the net capital costs of the PCS microcells will be amajor factor in the economic viability of PCS.

What has been suggested by a number of organizations is that existingcable television distribution plant be used to interconnect microcellequipment. Taking advantage of the broadband and the nearly ubiquitousnature of cable plant, it has been further proposed that the microcellequipment consist of simple RF repeaters that translate off-air mobilevoice traffic onto the cable plant and vice versa.

This approach uses the cable plant as a RF combining/splitting networksince it preserves the basic RF amplitude and phase/frequencyinformation. What has become apparent in tests is that this approach toPCS microcells yields both low capital costs and improved user service.

In summary, the low cost arises from the combination of simpletechnology, i.e. an RF repeater, using an existing asset base i.e. cableplant in a fashion that allows modulation/demodulation and publicswitched telephone network (PSTN) interface equipment to be centrallylocated. This allows these equipment costs to be amortised over a verylarge net coverage area.

The improved service arises from better call blocking probabilityassociated with the ability to centralize the base station equipmentrather than a priori allocation to specific microcells. Additionally,the cable plant can act to form distributed antenna arrays that can beshaped into "roamer corridors". Within these roamer corridors it is alsopossible to control the off-air dynamic range so as to reduce nearuser/far user interactions and line of sight blocking.

FIG. 1 illustrates the principal hardware elements and concepts of aprior art cordless telephone system employing base stations.

Base stations 1 operate at the off-air frequencies and performdemodulation and modulation functions for the telephone signals. Thebase stations 1 interface directly to twisted pair telecom lines.

The base stations 1 can be mounted to interface directly with nearbyhandsets (not shown), or can be located at a central site, as shown,where their ability to handle calls can be amortised over a largernetwork of microcells connected by TV cable plant, as mentioned above.

A remote antenna signal processor RASP 2 is located at the central siteand interfaces one of the base stations to cable plant 4.

Typically, signals from the base stations 1 travel over the cable plantto the handsets in the 200-450 Mhz band. Signals travelling in thereverse direction use the 5-30 Mhz return band on the cable plant.

Bi-directional distribution amplifiers 6 need to be compatible with thecable plant 4 and provide return band capability.

Remote antenna drivers (RADs) 8 must be compatible with existing TVcable plant and they may be configured for either coaxial cable or fiberplant.

RADs 8 pick-up the off-air signals and relay then back to a central sitevia the plant's return path, and also broadcast PCS signals on the cableforward path (200-450 Mhz) to nearby handsets, after suitable heterodyneoperations.

This prior art RAD-RASP design suffers a number of limitations, whichcomprise, specifically:

The need to operate where there is cable television plant. Cable TV maybe readily available for some residential markets, but less available ornot at all available in public and business markets.

The need for compatibility with existing cable TV services. Thisrequires the RAD-RASP units to use expensive heterodyne processing tointerface time division duplex off-air signals to the frequency divisionduplex cable TV plant.

The RAD-RASP arrangement is inappropriate in some markets, e.g. thoseserved by existing cordless base stations and those with predominatelyburied cable plant.

Furthermore, with such a system the voice quality within a distributedantenna can suffer some degradation from the differences in phase noiseof its constituent parts and from the differences in time delay of itsconstituent parts. In some circumstances, therefore, it is preferable touse RF repeaters, transferring signals by a time division duplexprotocol, instead of RADs, which employ frequency division duplexing.

Prior art RF repeaters have required two amplifiers, for amplifying thetransmit signals and the receive signals, respectively, in each RFrepeater.

In European Patent Application No. 442,259, there is disclosed aregenerative RF bi-directional communication system employing cascadedamplifier stages for periodically regenerating signals which aretransmitted and received along a series of radiating cable lengths,which link base station transceivers to hand-held or like mobilecommunication units. The amplifier stages are configured so that theoverall intermodulation generated by this system is substantiallyindependent of the number of the amplified stages and an intermediatefrequency distribution system is used so that the required level ofamplification is achieved through the cascaded amplifier stages at thelevel of low-power IF signals generated from the original RF signals inconjunction with appropriate oscillator and pilot signals. Thisrestricts the cascading effect occurring due to the plurality ofcascaded amplifier stages on the relatively low-power IF signals,thereby producing a negligible amount of intermodulation. It is,however, a disadvantage of such system that radio signals radiated fromone cable length may be received by an immediately preceding orsucceeding cable length and, therefore, may impair the signal carried bythe latter.

From French Patent 2482339, it is known to employ a radio link betweensuccessive stations.

U.S. Pat. No. 4,234,959 discloses a mobile repeater system in whichreception of a tone coded signal from a portable raises a squelchthreshold in two priority repeaters at adjacent locations, which are outof range of one another but not out of range out of each others portableunits. The portable-two-repeater range is thus decreased, withoutdecreasing the repeater-two-repeater range. Interference caused bysimultaneous transmission is eliminated, since only the appropriaterepeater is activated.

Disclosure of the Invention

It is an object of the present invention to provide a novel and improvedRF repeater for use in TDD cordless telephone systems, which avoids theneed for separate amplifiers for amplifying the transmit and receivesignals.

It is a further object of the present invention to provide a novel andimproved RF repeater arrangement employing a chain of TDD RF repeatersto form a roamer corridor along which a handset may travel whilemaintaining communications.

According to one aspect of the present invention, an RF repeater forinterfacing with a base station for exchanging transmit and receivesignals in a time division duplex cordless telephone system comprisesfirst signal exchange means for exchanging the transmit and receivesignals with the base station, second signal exchange means forexchanging the transmit and receive signals with a cordless handset, amulticarrier amplifier having an input and an output, and switch meansconnected to said amplifier output, said amplifier input and said firstand second signal exchange means and having first and second switchstates. The switch means connects the second signal exchange means tothe amplifier input and the amplifier output to the first signalexchange means in the first switch state and connects the first signalexchange means to the amplifier input and the amplifier output to thesecond signal exchange means in the second switch state. Also, means areprovided for controlling the operation of the switch means so that thetransmit and receive signals are alternately amplified by the amplifier.

In a preferred embodiment of the invention, a diode detector comparesthe receive signal and noise from a known noise source to provide an ACwaveform, which is then amplified and compared with a reference value bymeans of a comparator which, when the receive signal power is below apredetermined level, operates the switch means to squelch the receivesignal passed to the base station.

The RF repeater according to the present invention has a number ofadvantages.

Firstly, the number of amplifier elements required in the RF repeaterare reduced, and the overall cost and size of the RF repeater arecorrespondingly reduced.

In addition, the present invention affords excellent power efficiencysince the amplifier is always in use, while the repeater arrangement isin operation, whereas in the prior art RF repeaters, using separatetransmit and receive amplifiers, the amplifiers are used onlyperiodically, and for the rest of the time they consume power anddissipate heat without providing any benefit.

A further advantage of the present invention is that it can be readilyconfigured as an in-line RF repeater, i.e. it may be connected withother similar RF repeaters to increase the size of the coverage zoneserviced by the respective base station. Also, the voice quality in anydistributed antenna array provided by the RF repeaters need not sufferfrom degradation due to differential phase noise or differential timedelay.

According to another aspect of the present invention, there is providedan RF repeater arrangement for a time division duplex (TDD) cordlesstelephone system, comprising a chain of TDD RF repeaters which comprisesat least a first RF repeater and a second RF repeater, with a dedicatedsignal link for exchanging transmit and receive signals betweensuccessive ones of the RF repeaters in the chain. The first and secondRF repeaters each have a respective antenna for exchanging the transmitand receive signals with a TDD handset as radio signals, the antennashaving coverage zones which overlap to form a roamer corridor over whichthe handset can roam while maintaining radio communications with thefirst and second RF repeaters.

Preferably, the signal link comprises means for exchanging radio signalsbetween the first and second RF repeaters, and the radio signalexchanging means may comprise means for exchanging the transmit andreceive signals between the first and second RF repeaters at the samefrequency at which said transmit and receive signals are exchangedbetween the first and second RF repeaters and the handset.

The means for exchanging radio signals may include a co-axial cableextending from the first or second RF repeaters for locating the radiosignal exchanging means and the antennas relative to one another so asto counteract signal leakage therebetween.

In another embodiment of the invention, the signal link comprises acable interconnecting the first and second RF repeaters.

The chain may terminate at a terminal RF repeater having no means forforming a signal link with any succeeding RF repeater, and signalamplifier means may be included in the signal link to permit increasedseparation of the first and second RF repeaters.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily apparent from the followingdescription when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 diagrammatically illustrates a prior an cordless telephone systemas described above;

FIG. 2 shows a block diagram of an RF repeater according to a firstembodiment of the present invention;

FIG. 3 shows a block diagram illustrating in greater detail a part ofthe RF repeater of FIG. 2;

FIG. 4 shows a block diagram of an RF repeater according to a secondembodiment of the present invention;

FIG. 5 shows a block diagram of a part of the RF repeater of FIG. 4;

FIG. 6 shows an arrangement of three of the RF repeaters, similar tothat of FIG. 4, connected in cascade by intermediate coaxial cables;

FIGS. 7 and 7A show block diagrams of two modifications of the RFrepeater of FIG. 4;

FIG. 8 shows a circuit diagram of part of the RF repeater of FIG. 7;

FIGS. 8A and 8B show wave forms of signals in the circuit of FIG. 8;

FIG. 9 and 9A show modifications of the RF repeater of FIG. 2 for use ason-channel repeaters;

FIG. 10 shows a block diagram of a further modified RF repeater;

FIG. 11 shows a block diagram of a component of the RF repeater of FIG.10;

FIG. 12 diagrammatically illustrates the use of a time delay in anarrangement of two RF repeaters;

FIG. 13 shows an RF repeater arrangement with a base stationcommunicating by a radio link with an RF repeater; and

FIG. 14 shows an RF repeater arrangement employing a coupled antennapair.

BEST MODE FOR CARRYING OUT THE INVENTION

The RF repeater illustrated in FIG. 2 and indicated generally byreference numeral 10, has a coaxial cable input and output 12 connectedto a component 14 which is in turn connected to one terminal of atransfer switch 16. A coaxial cable (not shown) forms a signal conduitfrom a base station (not shown) to the cable terminal 12.

The transfer switch 16 has three other switch terminals, of which twoare connected to the input and the output, respectively, of an amplifier18, while the third is connected through a band limiting filter 20 to anantenna 22.

The transfer switch 16 has two switch states.

In the first switch state, as illustrated in broken lines in FIG. 2, thetransfer switch 16 connects the component 14 to the input of theamplifier 18, and also connects the output of the amplifier 18 to theband limiting filter 20 and the antenna 22.

In its second switch state, the transfer switch 16 connects thecomponent 14 to the output of the amplifier 18, and also connects theantenna 22, through the band limiting filter 20, to the input of theamplifier 18.

It will be apparent that, in the first switch state of the transferswitch 16, the amplifier 18 serves to amplify a transmit signal passingfrom the coaxial cable to the antenna 22, whereas in the second switchstate, the transfer switch 16 serves to amplify an incoming receivesignal passing from the antenna 22 to the coaxial cable.

The component 14 is illustrated in greater detail in FIG. 3, in which apower pickup 24 is shown, which serves to supply power to the component14.

FIG. 3 also shows a transmit/receive switching logic circuit 26 which,together with the power pickup 24, is connected through an RF choke 28to a conductor 30 and which control the changeovers of the switch stateof the transfer switch 16 in response to timing signals from thebasestation.

The coaxial cable input and output terminal 12 is connected to adirectional tap 32 at one end of the conductor 30, and the directionaltap 32 is also connected to a coaxial cable loop-through terminal 34, bywhich the RF repeater 10 can be connected in parallel with one or moreother such RF repeaters.

The directional tap 32 is connected through a DC blocking capacitor C1and a gain adjustment circuit 36 to the transfer switch 16.

The RF repeater of FIG. 2 may readily be simplified to serve as aterminator of the signal conduit comprising the coaxial cable (notshown) connected to the cable input and output terminal 12. For thispurpose, the directional tap 32 and the loop-through terminal 34 areomitted, and the cable input and output terminal 12 is connecteddirectly to the conductor 30.

The modification of the RF repeater illustrated in FIG. 4 and indicatedgenerally by reference numeral 10A has the component 14 replaced by acomponent 14A, which is connected to the transfer switch 16 and which isalso connected, through an RF choke 28A and a conductor 38, to a coaxialcable loop-through terminal 34A, which corresponds to the terminal 34 ofFIG. 3 and which is used for connecting the RF repeater 10A in line withone or more similar RF repeaters.

The conductor 38 is connected through a directional tap 32A to aconductor 40 which interconnects the transfer switch 16 and the bandlimiting filter 20.

As can be seen from FIG. 5, the conductor 30 is, in this case, connecteddirectly to the coaxial cable input and output terminal 12, and theoutputs of the power pick-up 24 and the transmit/receive switching logiccircuit 26 are connected at the output of the component 14A to theconductor 38.

FIG. 6 shows an arrangement of five RF repeaters 10A-10C arranged inline and connected to one another and to a coaxial cable input andoutput terminal 40, of the transfer switch 16 in for connection throughthe cable TV plant 4, serving as a first signal link, to the basestation. coaxial cables second signal links comprising 42A-42E, whichtypically may have a length of 400 feet, except for the coaxial cable42E, which may be longer and may, for example, be 500 feet in length.

As can be seen in FIG. 6, the RF repeaters 10B-10E are similar to the RFrepeater 10A. It is, however, alternately possible to replace these RFrepeaters by RF repeaters such as the RF repeater 10 of FIG. 2.

In embodiment of the invention shown in FIG. 6, the RF repeaters 10A-10Cand 10E are each provided with the antenna 22 for exchanging off-airsignals with the handsets (not shown). However, the RF repeater 10D isarranged and employed as a time division duplex line amplifier, toprovide gain on the coaxial cable 42E, and therefore has the bandpassfilter 20 connected to the coaxial cable 42E instead of to an antenna.

Also, the RF repeater 10E has no loop-through terminal.

As is also apparent from FIG. 6, the coverage zones 44A-44C of the RFrepeaters 10A-10C are arranged in a distributed antenna array, andoverlap one another, so that the cordless handsets communicating throughthe RF repeaters 10A, 10B and 10C can move from one of these zones toanother, without need for additional call hand-off processing.

FIG. 7 shows a modification, indicated generally by reference numeral10F, of the RF repeater 10A of FIG. 3. The modified RF repeater 10F hasan additional component 14B inserted between the output of the amplifier18 and the transfer switch 16.

The component 14B is a power detector circuit, which is provided fordetermining the power of the receive signal from the antenna 22 and forsquelching the RF repeater when the power falls below a predeterminedvalue. In an alternative embodiment, which is not shown, the powerdetector circuit 14B may be inserted within the interstage gain elementsof the amplifier 18.

As shown in FIG. 8, the power detector circuit 14B is connected to theamplifier 18 and the transfer switch 16 through a directional tap 46. Aswitch control 48 serves to connect the signal and noise at the tap 46,and a known noise source 50, to the input of an RF amplifier 52.

An oscillator 53 provides a switch control waveform S₁ (FIG. 8A) to theswitch control 48, so that the RF amplifier 52 alternately receives asample signal S₂ (FIG. 8B) from the known noise source 50 and the signaland noise, indicated by S₃, from the tap 46.

The output of the RF amplifier 52 is connected to a diode detectorcircuit indicated generally by reference numeral 54, which rapidlysamples both the band limited RF signal and noise S₃ from the tap 46 andthe sample signal S₃ from the known noise source 50.

As a consequence of the switching action of the switch control 48, an ACbaseband waveform, which is illustrated in FIG. 8b, is produced at pointP at the output of the diode detector circuit 54.

The detector output signal has a period t which is defined by the switchcontrol 48, and has an amplitude A, which corresponds to the level ofthe signal and noise passing through the tap 46 from the amplifier 18 incomparison to the level of the sample signal S₂ from the known noisesource 50. The period t is selected to be sufficiently large to allowthe operational amplifier 52 to have gain at the switching rate and tobe sufficiently small so as to not interact with the time divisionduplex signal rates of the transmit and receive signals.

This signal is then amplified by an operational amplifier circuit 56,which has a large AC gain at the switching frequency, and the output ofwhich is connected to one terminal of a comparator 58.

A reference voltage V_(T) is applied to the other input of thecomparator 58, which compares the two values to provide an output signalon a comparator output 60. If the amplitude A is insufficient to exceedthe threshold voltage V_(T), the comparator output signal causes thetransfer switch 16 to squelch the received signal that would otherwisebe passed back over the coaxial output.

For squelch operation in a time division duplex amplifier, thisarrangement presents a number of advantages:

1. Amplification of the AC baseband allows very large operationalamplifier gains to be used without causing trouble with DC offsets orvoltage rail limitation. Also, variations in the performance of thediode detector circuit 54 are of little consequence, since thecomparator action depends on the diode performance referenced againstthe known noise source 50. Consequently, this arrangement is extremelysensitive and, therefore, suitable for squelch operations, that do notuse complex heterodyning processing.

2. By locating the diode detector circuit 54 in the amplifier chainconnected to the transfer switch 16, the diode detector circuit 54 canbe used to measure power directed towards the antenna 22. This allowsthe possibility of employing the circuit for installation and settingup, and also automatic control, of the net amplifier gain.

3. The circuit can be used for automatic gain control of the gain in thereverse direction.

4. This arrangement utilizes low cost, simple components, particularlyif coupled to microprocessor control of the comparator and switchingfunctions. It is pointed out that the transfer switch 16 provides aneasy and effective way to effect the squelching.

Since the amplifier 18 is not connected to the coaxial cableinput/output terminal 12, it does not inject noise in the coaxial cablewhen the squelch is active.

In addition, it is pointed out that the RF repeater 10 of FIG. 2 can bemodified by inclusion of the power detector circuit 14B between theamplifier 18 and the transfer switch 16 of FIG. 2.

The RF repeater 10F of FIG. 7 may be modified, as illustrated in FIG.7A; so as to serve as a time division duplex line amplifier in thesignal conduit comprising the coaxial cable (not shown) connected to thecoaxial cable input and output terminal 12. For this purpose, theantenna 22, the band limiting filter 20 and the directional tap 32A ofFIG. 7 are omitted, and the transfer switch 16 is connected by conductor61 to a further coaxial cable input and output terminal 34C. A furthercoaxial cable (not shown) is connected, as part of the signal conduit,between the terminal 12B and a further RF repeater (not shown) which maybe similar, for example, to the RF repeater 10F of FIG. 7.

FIG. 9 shows an RF repeater, indicated generally by reference numeral10G, which is a further modification of the RF repeater 10 of FIG. 2.

More particularly the RF repeater 10G of Fibre 9 includes a power supply24 for locally applied power and a timing control circuit 26A forgenerating locally the timing pulses for controlling the operation ofthe RF repeater. The timing control circuit 26A is connected to thesignal conduit through a directional tap 32B.

Local timing is effected in this embodiment by means of control andsignalling channels containing timing data.

It is, however, alternatively possible to employ local cellular, pagingor TV signals to derive the timing for both the base stations and theoff-air repeater.

In this embodiment, the base station, which is indicated by referencenumeral 1A, communicates with the RF repeater 10E through antennas 62Aand 62B having directional gain, and the RF repeater 10E in turncommunicates with a further RF repeater through antennas, of which onlyone is shown and which is indicated by reference numeral 62C, whichlikewise have directional gain.

A modified arrangement of this type is illustrated in FIG. 9A, in whichthere is shown a further modified RF repeater 10H, with the timingcontrol circuit 26A connected to antenna 62D. In this case, a furthertiming control circuit 26B is connected to the base station 1B, andprovided with an antenna 62E. The antennas 62D and 62E serve to receivethe local paging or cellular signals, or TV signals.

In order to avoid possible signal leakage between the antennas 62C and22, a length of co-axial cable may be inserted between the RF repeater10H and the antenna 62C so as to counteract such leakage by physicalseparation of the antennas 62C and 22 allowed by the length of the cableand/or the physical location of the antennas, and thus the relativelocation of the antennas, which may be arranged so as to locate abuilding or other obstruction between the antennas 62C and 22. In thisway, it can be ensured that the coupling between the antennas is lessthan the gain of the RF repeater 10H, so that feedback problems areavoided. Similar measures may be taken to reduce or avoid couplingbetween the other antennas of the arrangement shown in FIG. 9A and alsobetween the antennas of FIG. 9 and other embodiments of the presentinvention employing a signal link for exchanging the transmit andreceive signals between RF repeaters and/or between an RF repeater and abase station or other component.

Also, while RF repeaters normally receive and output their signals atthe same frequency, it may in some circumstances be advantageous toemploy heterodyning in the signal links between RF repeaters and/or anRF repeater and its base station, and it is accordingly to be understoodthat the expression "RF repeater" as employed herewith may includeheterodyne repeaters.

The embodiments of FIGS. 9 and 9A may usefully be employed, for example,when the off-air connection between the base station and the RF repeateris used to communicate over an intermediate area in which there is noright of way for coaxial cable or over which, for some other reason, itis not possible to employ co-axial cable, e.g. as described below withreference to FIG. 13.

An additional use for embodiments of FIGS. 9 and 9A is to provide forenhanced in-building mobile telephoning from a Base Station (or RAD),located outside the building. In this application, the antenna 62B islocated exterior to the building and communicates with the base station,while antenna 22 is inside the building. For such in-buildingapplications, power is locally available (e.g. 110v as power outlet),and cable TV outlets may also provide the timing signals necessary tosynchronize the base station and the RF repeaters.

The RF repeaters 10G and 10H may be modified for connection to one ormore further RF repeaters as described above.

FIG. 10 shows a further embodiment of the RF repeater according to thepresent invention, indicated generally by reference numeral 10I, andwhich is similar to the RF repeater 10A of FIG. 7A except that, in thecase of the RF repeater 10I, the coaxial cable input and output terminal12 is replaced by an antenna 22A, the component 14B is replaced by thecomponent 14C, illustrated in FIG. 11, the antenna 22 is omitted and theband limiting filter 20 is connected to the loop-through terminal 34C.

Referring to FIG. 11, it will be seen that the signal conduit isconnected through a directional tap 32C to a timing control circuit 26B,the output of which is connected to the transmit/receive switching logic26.

The RF repeater 10I may serve as an off-air relay communicating with abase station, and also providing power and synchronization andcommunicating with further RF repeaters through the loop-throughterminal 34A which is connected to a dedicated coaxial cable (notshown).

FIG. 12 illustrates a handset 64 which is located in the so-called"overlap zone" between the coverage zones 66A and 66B of respective RFrepeaters 10J and 10K, which are connected to a base station 1B.

In such circumstances, it is possible for phasing effects to create a"null" in the overlap region, which varies in severity according to thedifferences in phase noise associated with the two RF repeaters 10F and10G. By using a dedicated signal conduit, with no heterodyne operations,this differential phase noise is made negligible, thus improving voicequality.

Also, differential timing effects affect voice quality in the overlapzone. The time division duplex timing of the RF repeater 10J isdependent on the propagation delay of the path from point X to thehandset 64. However, the analogous path for the RF repeater 10K is fromthe point X, through the point Y to the handset 64. To counteract theeffect of these different point lengths, a time delay dement 68 isprovided between point X and the RF repeater 10J. Without this timedelay element 68, when the handset 64 is in the location in which it isshown in FIG. 12, it would be subjected to two versions of time divisionduplex timing, the two versions differing by an amount equivalent to thedelay path XY. The magnitude of the time delay of the time delay elementis selected so as to equalize the timing on the two paths.

FIG. 13 shows a further possible embodiment of the present invention, inwhich a base station communicates by off-air (radio) signals with an RFrepeater 10L over a highway 70. This arrangement avoids any necessityfor a right of way between the base station 1C and the RF repeater 10L.

The RF repeater 10L is connected to a coaxial cable 72 to a further RFrepeater 10M, which in turn is connected by a coaxial cable to a stillfurther RF repeater 10N. The RF repeaters 10L-10N are implemented asdescribed above with reference to the preceding figures.

The length of the coaxial cable 72 is sufficient to ensure RF stability,i.e. that there is no feedback from RF repeater 10L to RF repeater 10Mor from RF repeater 10N to RF repeater 10L. Thus, for example, repeater10L may be in a mode of receiving signals from the base station 10Cwhile simultaneously relaying the signals and broadcasting them throughRF repeaters 10M and 10N.

Because of the isolation afforded by the distance between the RFrepeater 10L and the RF repeaters 10M and 10N, directive antennas arenot a necessity, for operational stability in this arrangement.

As will be apparent to those skilled in the art, various modificationsmay be made in the above described embodiments of the invention withinthe scope of the appended claims. For example antenna diversity may beemployed at the RF repeater by adding a second switched antenna,commanded by a base station.

However switched-antenna diversity is awkward in an RF repeaterarrangement, because in many instances the base station needs access tosignals from both antennas, necessitating the use of two coaxial cableruns and two RF repeaters.

An alternate arrangement, which has been found by the inventor to givenearly as good performance as switched antenna diversity, is shown inFIG. 14.

In FIG. 14, the RF repeater communicates with local handsets (not shown)via the first antenna 80A, which is connected to the RF repeater via thethrow leg 82 of a conventional 10 db. directional coupler 84. Howeverthe coupled leg is also connected to a second antenna 80B, physicallylocated some distance from the first antenna.

Should a mobile handset move into a multipath null of the first antenna81A, this will typically cause the signal level at the RF repeater todrop 20-30 db, potentially destroying the RF link. However it isunlikely that the handset location would also be a multipath null forthe second antenna 81B, with the consequence that the composite drop insignal level will be only 10 db, and thus the link will be sustained.

The selection of a 10 db coupler is preferred because large couplingvalues (e.g. 20 db), will give poor composite multipath performance,while smaller coupling values (e.g. 3 db), will cause the two antennas81A and 81B to interact and substantially shape the composite antennapattern.

While the above-described embodiments of the invention do not employheterodyne operation, it is envisaged that such operation may beemployed in implementing the present invention, particularly for mobiletelephoning where the RF signal is at a very high frequency (e.g. 1.9GHz), and as a consequence the coaxial cable losses associated with onefrequency RF repeaters are high.

I claim:
 1. A time division duplex RF repeater arrangement comprising:afirst time division duplex RF repeater; a first signal link forexchanging time division duplex transmit and receive signals betweensaid first time division duplex RF repeater and a basestation; a secondtime division duplex RF repeater; a second signal link for exchangingthe transmit and receive signals between said first and second timedivision duplex RF receivers; said first and second time division duplexRF receivers each having an antenna for exchanging the transmit andreceive signals with a mobile cordless time division duplex handset asradio signals; and said antennas having coverage zones which overlap oneanother; each of said first and second time division duplex RF repeatershaving a single amplifier and a transfer switch connected to pass thetransmit signals to said amplifier in a first switch state of saidtransmit switch and to pass the receive signals to said amplifier in asecond switch state of said transmit switch, whereby the transmitsignals and the receive signals are amplified by said single amplifier.2. A time division duplex RF repeater arrangement as claimed in claim 1,wherein said first and second time division duplex RF repeaters eachincludes means responsive to timing signals from the basestation forcontrolling changeover of its transfer switch from the first switchstate to the second switch state and vice versa.
 3. A time divisionduplex RF repeater arrangement as claimed in claim 1, wherein at leastone of said first and second time division duplex RF repeaters islocated within a building for providing communication within thebuilding, and wherein a remote antenna is provided at the exterior ofthe building and a further signal link connects said remote antennadriver to one of said first and second time division duplex RF repeatersfor exchanging the transmit and receive signals with the latter.
 4. Atime division duplex RF repeater arrangement as claimed in claim 1,wherein said first signal link comprises a cable TV plant.
 5. A timedivision duplex RF repeater arrangement as claimed in claim 1, whereinsaid second signal link comprises means for exchanging the transmit andreceive signals as radio signals between said first and second timedivision duplex RF repeaters.
 6. A time division duplex RF repeaterarrangement as claimed in claim 5, wherein said radio signal exchangingmeans comprise means for exchanging the transmit and receive signalsbetween said first and second time division duplex RF repeaters at thesame frequency at which the transmit and receive signals are exchangedbetween said first and second time division duplex RF repeaters and themobile cordless handset.
 7. A time division duplex RF repeaterarrangement as claimed in claim 5, including co-axial cable extendingfrom said first time division duplex RF repeaters for locating saidradio signal exchanging means and said antenna of said first timedivision duplex RF repeater relative to one another so as to counteractsignal leakage therebetween.
 8. A time division duplex RF repeaterarrangement as claimed in claim 1, wherein said second signal linkcomprises a co-axial cable connecting said first and second timedivision duplex RF repeaters.